Marine diesel engines power the majority of ships used for marine transportation. These engines typically burn Heavy Fuel Oil (HFO), which contains high concentrations of sulfur and other impurities. The combustion process produces high concentrations of sulfur oxides (SOX), nitrogen oxides (NOX), carbon oxides (COX) such as C02, and other gases that are subject to increasing restrictions with new emerging emissions requirements.
One approach to reducing marine engine emissions is to switch to higher purified fuels, or distillates. These distillates are more expensive than HFO. An alternative is to post-treat, clean, or scrub the combustion exhaust gasses before they are discharged into the atmosphere.
Sea water scrubbers have been developed as a post-treatment solution to clean marine engine exhaust. A commonly used process is to spray aqueous alkaline or ammonia sorbents into the exhaust stream. However, these ‘wet’ sea water scrubbers can require large amounts of water and consequently generate large amounts of waste water, which can include metal salts such as calcium sulfate, soot, oils, and heavy metals. This can produce a toxic sludge that requires complex on board water treatment, and as well as disposal of sludge at designated ports. The resultant system is large, complex, expensive and energy intensive, increasing ship fuel consumption by as much as three percent. Although conventional sea water scrubber systems may be well suited for fixed land based power plants, they are simply too large and complex to operate efficiently in a marine application. As well, such systems may not be well suited to removing C02 from marine engine exhaust.
Treatment of marine exhaust could in principle be accomplished by modifying existing land-based technology to bubble marine exhaust gases through an ionic liquid. However, this approach may not be practical due to the high flow rates of marine exhaust and the resultant large volume of ionic liquid required, in light of the space and weight constraints of a marine vessel. The energy required to compress the exhaust gases to bubble through the ionic liquids could exceed the total energy available from the ship.
A system for scrubbing marine engine exhaust gasses using membrane technology has been proposed in Chinese patent No 200710012371.1.
An object of the present invention is to provide an improved method and system for reducing the concentration of one or more target emission gasses from a source such as a marine diesel engine.